What is a ceramic capacitor?

Ceramic capacitors are compact components capable of rapid energy discharge. A frequently asked question regarding ceramic capacitors is: "When purchasing multilayer ceramic capacitors (MLCCs), what actual capacitance value can be obtained?" This may sound unusual, but the actual capacitance value is not the nominal value specified in the datasheet.   

Factors Affecting Capacitance:   

• Tolerance   

• Temperature coefficient   

• Dielectric type   

• DC bias voltage (can significantly reduce capacitance)   

The effective capacitance may only reach 50% of the nominal value stated in the datasheet.   

Critical Consideration:   

"How much capacitance is truly needed?"   

For ceramic capacitors, the absolute capacitance value is less important than ensuring the energy transfer speed meets the application's frequency requirements. For example, if conducted emission tests fail at 100MHz, select a capacitor with the lowest impedance at that frequency.   

Common Misconception:   

Engineers often focus on selecting low-ESR/ESL ceramic capacitors but neglect PCB layout. In reality, the inductance of PCB traces (not the MLCC's ESL) dominates high-frequency impedance.   

Ceramic Capacitor Challenges:   

• Low-ESR surface-mount devices   

• Prone to resonance with PCB trace inductance   

• Even short traces can form resonant circuits above 100MHz   

Resonance Mitigation Methods:   

1. Use high-ESR capacitors   

2. Add a small series resistor (e.g., 1Ω)   

3. Adjust capacitance to shift resonant frequency   

Ceramic Disc Capacitors (Y2 Class)   

Typical Applications:   

• Common-mode noise filtering (appliances, automotive, industrial)   

• EMI suppression   

• Primary-to-secondary circuit isolation   

Key Considerations:   

1. Leakage Current:   

   • Flows through ground paths   

   • Potential safety hazard   

2. Safety Standards:   

   • Capacitance values strictly regulated by safety certifications